Clinical data from 12 and 13 year old Icelanders (n=1032) obtained in 1984 were compared with those obtained for 12 and 13 year olds in the 1980 and 1986 NIDR National Children's Surveys (n=3256 and n=3460, respectively) for the US population. The surface-specific caries attack rates were consistently higher for the Icelandic population, in many instances 4 to 10 times as high. The notable difference was the strong inverse relationship observed between fluoride exposure and the level of smooth surface caries between the two groups. Also noticed was that the prevalence of dental caries is rapidly becoming a pit and fissure phenomenom in the US population.